Anyone Else Experience Driver Update Issues?

I recently updated my drivers from OpenGL 3.2 to 4.3 and it seems to be interpreted differently. I was convinced this shouldn't impact legacy OpenGL.

For example, when using a FBO to render to a texture of type GL_UNSIGNED_SHORT_5_6_5 in OpenGL 3.2 the quality was good. But after updating to 4.3 the quality is poor and blotchy. I changed this to GL_UNSIGNED_SHORT and it seems to have fixed it but there are a bunch of other issues I'm witnessing as well.

Has anyone else experienced anything similar to this?

I am using the fixed function pipeline as well as programmable and wonder if that has anything to do with it.

A possible explanation is your hardware vendor tightening up their conformance. In older OpenGL your vendor may have been silently promoting your requested 565 format to something with greater precision, which is allowed; with the 4.3 driver, when you ask for a 565 format that might just be exactly what you get.